<template>
	<div>
		<ul class="list">
			<li class="item" 
				v-for="item in letters" 
				:key="item"
				:ref="item"
				@click="handleClick"
				@touchstart="touchStart"
				@touchmove="touchMove"
				@touchend="touchEnd"
			>
				{{item}}
			</li>
		</ul>
	</div>
</template>

<script>
	export default{
		name:'CityNav',
		props:{
			cities:{
				type:Object,
				default:{}
			}
		},
		data(){
			return{
				touchStatus:false,
				startY:0,
				timer:null
			}
		},
		computed:{
			letters(){
				const letters = []
				for(let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		methods:{
			handleClick(e){
				this.$emit('change',e.target.innerText)
			},
			touchStart(){
				this.touchStatus = true
			},
			touchMove(e){
				if(this.touchStatus){
					if(this.timer){
						window.clearInterval(this.timer)
					}
					this.timer = window.setInterval(()=> {
						const touchY = e.touches[0].clientY - 79
						const index  = Math.floor((touchY - this.startY) / 20)
						if(index >= 0 && index < this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)

				}
			},
			touchEnd(){
				this.touchStatus = false
			},
			updated(){
				this.startY = this.$refs['A'][0].offsetTop
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/common.styl'
	.list
		display:flex
		flex-direction:column
		justify-content:center
		position:absolute
		top:1.58rem
		right:0
		bottom:0
		width:.4rem
		.item
			line-height:.4rem
			text-align:center
			color:$bgColor
</style>